Engine systems may include one or more pressure transducers at various locations for measuring engine operating parameters such as manifold pressure (MAP), exhaust pressure, boost pressure, barometric pressure, etc. The measured parameters are then used to control engine settings. For example, based on the measured parameters, the settings of various engine actuators may be adjusted, such as the operation of an intake throttle, exhaust catalyst, turbocharger, particulate filter, etc. In addition, the measurements affect engine controls for exhaust emissions and engine fuel economy. Various pressure transducer designs are available including, for example, piezo-resistive-type (PRT) transducers and capacitor-type transducers. However, such transducers may have short lives due to the harsh environment they are located in. This is particularly true in the case of exhaust pressure transducers. For example, capacitor-type and PRT transducers may become degraded due to their circuitry being exposed to corrosive liquids. Since the measurement provided by the transducers significantly affects engine control, such transducers may need frequent replacement to allow for reliable readings.
One example of an exhaust transducer that has an improved performance is provided by Goto et al. in U.S. Pat. No. 8,208,143. Therein, an exhaust sensor uses an optical fiber for irradiating exhaust gas with laser light the light irradiated across the exhaust path. The light, upon transmission through the exhaust gas, is measured by a detector. Based on the light received by the detector, various exhaust gas parameters, such as concentration, temperature, etc., are determined. In still other examples, strain gauge type pressure transducers whose resistance value changes with deformation of the sensor may be used. Therein, the amount of deformation of the sensor is correlated with pressure in the vicinity of the sensor.
However, the inventors herein have recognized potential issues with such approaches. As an example, such transducers may still be susceptible to corrosion from exhaust components. For example, due to the sensor substrate being coupled across a cross-section of the exhaust passage, it may degrade easily due to contact with high temperature exhaust and corrosive exhaust gas components. As a result, even if the laser is functional, the sensor may need to be replaced. Further, having the detector in the exhaust environment makes its view of the light source prone to obstruction by soot. Consequently, there may still be expensive warranty issues. In addition, there may be a possibility of needing to recall an engine component, reducing a customer quality perception of the vehicle manufacturer. As another example, the sensors may be cost-prohibitive. For example, strain gauge transducer assemblies, when assembled into a sealed diaphragm, may involve stringent cleaning of the mounting surface and manual application of the strain gauge to the diaphragm with a bridge adhesive. Then the remaining area may need to be filled with a potting compound. The multiple steps add cost and complexity which may render the sensor too costly.
In one example, some of the above issues may be addressed by a method for an engine, comprising: adjusting engine operation responsive to laser pulses received bouncing off a diaphragm in an engine manifold. In this way, a pressure sensor may be provided within a diaphragm that is deflected by pressure variations in the engine manifold.
As an example, an engine manifold may be configured to include a laser pressure transducer system. The laser pressure transducer system may include a hollow diaphragm that is coupled to the engine manifold. For example, the diaphragm may be molded into an engine intake manifold for estimating an intake manifold pressure. As another example, the diaphragm may be mounted on or stamped onto an exhaust manifold for estimating an exhaust manifold pressure. A diode laser and a laser detector may be mounted to a top of the diaphragm. For example, the laser and detector may be mounted to a housing that holds the diaphragm in the engine manifold. The inner cavity of the diaphragm may be sealed, reducing the need for frequent and stringent cleaning. The laser may be operated to emit laser pulses at a pre-defined frequency into the interior (and towards the bottom) of the diaphragm. The pulses may then reflect off the interior and bounce back towards the top, where they may be detected by the detector. A deformation of the diaphragm may be determined based on a time elapsed between emission of the laser pulse from the laser, and detection of the reflected pulse at the detector. The elapsed duration may be compared to a threshold duration learned during calibration conditions when the diaphragm is known to have no deformation (such as during an engine-off condition). As the elapsed duration decreases relative to the calibrated threshold, the estimated deformation of the diaphragm may increase. Further, the deformation estimate may be adjusted based on a temperature of the diaphragm as determined by a thermal sensor mounted on the diaphragm, alongside the laser and detector. The thermal sensor may estimate the diaphragm temperature based on the sensing of infra-red radiation received from inside the diaphragm. The estimated deformation of the diaphragm may be directly correlated with an amount of manifold pressure experienced by the diaphragm. In some embodiments, alongside the static pressure measurement, the output of the laser may also be used to perform a Doppler shift analysis of the diaphragm's deflection, thereby providing a higher resolution dynamic pressure measurement. One of more engine operating parameters, such as throttle opening and boost pressure, may then be adjusted based on the manifold pressure estimate. By using a laser pressure transducer, each of the static pressure measurement and dynamic pressure measurement may be achieved with the same pressure transducer. As such, Doppler shift analysis of manifold pressure may be outside the capability of conventional strain-gage pressure sensors.
In this way, a more cost-effective manifold pressure transducer/sensor may be provided without compromising the accuracy or reliability of the sensor. By using lasers, detectors, and thermal sensors that are coupled to a sealed diaphragm, the sensor circuitry can be protected from the harsh environment of the engine intake or exhaust manifold, improving sensor durability and reducing warranty issues. By relying on laser components that can be assembled easily (e.g., circuitry that can be assembled with pick and place machines onto a single circuit card), the cost and complexity of assembling a pressure transducer into an engine intake or exhaust manifold can be reduced. By improving the reliability of the pressure measurement, engine control errors may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.